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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Cold Trap Replacement Project Report

This report documents the replacement of the Mechanisms Engineering Test Loop (METL) cold trap. The work involved preparation of the facility to replace the cold trap, removal of the existing welded cold trap from the sodium purification circuit, installation of a new replacement cold trap, completion of associated welds and examinations, restoration of instrumentation and heaters, and controlled return of the cold trap circuit to service. The replacement represented a significant maintenance evolution because the cold trap is an integral welded component of the sodium system. As a result, the work required coordinated control of sodium chemistry, deliberate formation of freeze plugs, inert gas management, precision cutting and welding, and a staged reheating and refill sequence. The activity was executed using procedural controls intended to protect personnel, preserve system cleanliness, and maintain the integrity of the sodium boundary throughout the work. This report provides a narrative summary of the milestone, including the purpose of the work, the pre-job system condition, the major field activities performed, observations made during execution, and the resulting post-work condition of the METL cold trap circuit.

42 ENGINEERING↗
DOE OSTI2024

Predicting synthetic mRNA stability using massively parallel kinetic measurements, biophysical modeling, and machine learning

Abstract mRNA degradation is a central process that affects all gene expression levels, though it remains challenging to predict the stability of a mRNA from its sequence, due to the many coupled interactions that control degradation rate. Here, we carried out massively parallel kinetic decay measurements on over 50,000 bacterial mRNAs, using a learn-by-design approach to develop and validate a predictive sequence-to-function model of mRNA stability. mRNAs were designed to systematically vary translation rates, secondary structures, sequence compositions, G-quadruplexes, i-motifs, and RppH activity, resulting in mRNA half-lives from about 20 seconds to 20 minutes. We combined biophysical models and machine learning to develop steady-state and kinetic decay models of mRNA stability with high accuracy and generalizability, utilizing transcription rate models to identify mRNA isoforms and translation rate models to calculate ribosome protection. Overall, the developed model quantifies the key interactions that collectively control mRNA stability in bacterial operons and predicts how changing mRNA sequence alters mRNA stability, which is important when studying and engineering bacterial genetic systems.

Cetnar, Daniel P.↗
DOE OSTI2020

Portable Rabies Virus Sequencing in Canine Rabies Endemic Countries Using the Oxford Nanopore MinION

As countries with endemic canine rabies progress towards elimination by 2030, it will become necessary to employ techniques to help plan, monitor, and confirm canine rabies elimination. Sequencing can provide critical information to inform control and vaccination strategies by identifying genetically distinct virus variants that may have different host reservoir species or geographic distributions. However, many rabies testing laboratories lack the resources or expertise for sequencing, especially in remote or rural areas where human rabies deaths are highest. We developed a low-cost, high throughput rabies virus sequencing method using the Oxford Nanopore MinION portable sequencer. A total of 259 sequences were generated from diverse rabies virus isolates in public health laboratories lacking rabies virus sequencing capacity in Guatemala, India, Kenya, and Vietnam. Phylogenetic analysis provided valuable insight into rabies virus diversity and distribution in these countries and identified a new rabies virus lineage in Kenya, the first published canine rabies virus sequence from Guatemala, evidence of rabies spread across an international border in Vietnam, and importation of a rabid dog into a state working to become rabies-free in India. Taken together, our evaluation highlights the MinION’s potential for low-cost, high volume sequencing of pathogens in locations with limited resources.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Searching for Grid-Forming Technologies That Do Not Impact Protection Systems: A promising technology

The design of legacy-line protection elements has been guided by the behavior of synchronous machines during faults. Because of the significant field-winding inductance and rotating mass, the magnitude, angular frequency, and phase angle of the back-electromotive force (EMF) voltage waveforms of synchronous machines remain practically constant for several hundreds of milliseconds after a fault occurs. Furthermore this has facilitated the engineering of the memory-polarization technique in mho distance elements, which has been effective for machine-dominant power grids. However, this assumption is no longer held for inverter-based resources (IBRs) because of the lack of field winding and moment of inertia in power electronics devices. Notably, the negative-sequence directional overcurrent protection and the quadrilateral distance elements have been impacted by early IBRs with grid-following (GFL) controls because they did not inject negative-sequence currents during asymmetrical faults.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

On the Low Risk of SSR in Type III Wind Turbines Operating in Grid-Forming Control: Preprint

We have shown in a previous work that the risk of sub-synchronous resonance (SSR) between a wind power plant with Type III wind turbines and series-compensated transmission lines is low when the wind turbines in the plant are operated in grid-forming mode, instead of the standard grid-following mode. The fundamental mechanism behind the improved damping characteristics is explained in this paper by modeling the positive and negative sequence impedances of Type III wind turbines for GFM operation mode. It is discovered that the GFM control naturally acts against the negative resistance of Type III wind turbines that results from an interaction between the proportional gain of the rotor-side converter current controller and negative slip. The developed sequence impedance models and improved damping behavior are verified using PSCAD simulations of a 2.5-MW Type III GFM wind turbine. The modeling predictions are also supported by experimentally measuring the sequence impedance response of a 2.5-MW Type III wind turbine during operation in GFL and GFM modes.

grid-following turbine↗
DOE OSTI2022

Formal verification and validation of run-to-completion style state charts using Event-B

State chart notations with ‘run to completion’ semantics are popular with engineers for designing controllers that react to environment events with a sequence of state transitions but lack formal refinement and rigorous verification methods. State chart models are typically used to design complex control systems that respond to environmental triggers with a sequential process. The model is usually constructed at a concrete level and verified and validated using animation techniques relying on human judgement. Event-B, on the other hand, is based on refinement from an initial abstraction and is designed to make formal verification by automatic theorem provers feasible. Abstraction and formal verification provide greater assurance that critical (e.g. safety or security) properties are not violated by the control system. In this paper, we introduce a notion of refinement into a ‘run to completion’ state chart modelling notation and leverage Event-B’s tool support for theorem proving. We describe the difficulties in translating ‘run to completion’ semantics into Event-B refinements and suggest a solution. We illustrate our approach and show how models can be validated at different refinement levels using our scenario checker animation tools. We show how critical invariant properties can be verified by proof despite the reactive nature of the system and how behavioural aspects of the system can be verified by testing the expected reactions using a temporal logic, model checking approach. To verify liveness, we outline a proof that the run to completion is deadlock-free and converges to complete the run.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Implication of rare genetic variants of NODAL and ACVR1B in congenital heart disease patients from Indian population

Highlights: • Screening of 300 CHD patients revealed two rare missense variants (p.P51L & p.D327E) in NODAL. • A novel missense variation p.M345I was identified in ACVR1B. • Bioinformatic analyses suggested that these variants could have deleterious role. • Three-dimensional modelling suggested conformation changes in the mutated proteins compared to wild-type. • In vitro studies demonstrated that missense variants affect the function of NODAL and ACVR1B. NODAL signaling plays an essential role in vertebrate embryonic patterning and heart development. Accumulating evidences suggest that genetic mutations in TGF-β/NODAL signaling pathway can cause congenital heart disease in humans. To investigate the implication of NODAL signaling in isolated cardiovascular malformation, we have screened 300 non-syndromic CHD cases and 200 controls for NODAL and ACVR1B by Sanger sequencing and identified two rare missense (c.152C > T; p.P51L and c.981 T > A; p.D327E) variants in NODAL and a novel missense variant c.1035G > A; p.M345I in ACVR1B. All these variants are absent in 200 controls. Three-dimensional protein-modelling demonstrates that both p.P51L and p.D327E variations of NODAL and p.M345I mutation of ACVR1B, affect the tertiary structure of respective proteins. Variants of NODAL (p.P51L and p.D327E) and ACVR1B (p.M345I), significantly reduce the transactivation of AR3-Luc, (CAGA){sub 12}-Luc and (SBE){sub 4}-Luc promoters. Moreover, qRT-PCR results have also deciphered a reduction in the expression of cardiac-enriched transcription factors namely Gata4, Nkx2-5, and Tbx5 in both the mutants of NODAL. Decreased expression of, Gata4, Nkx2-5, Tbx5, and lefty is observed in p.M345I mutant of ACVR1B as well. Additionally, reduced phosphorylation of SMAD2/3 in response to these variants, suggests impaired NODAL signaling and possibly responsible for defective cell fate decision and differentiation of cardiomyocytes leading to CHD phenotype.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

Achieving designed texture and flows in bulk active nematics using optimal control theory

Being intrinsically nonequilibrium, active materials can potentially perform functions that would be thermodynamically forbidden in passive materials. However, active systems have diverse local attractors that correspond to distinct dynamical states, many of which exhibit chaotic turbulent-like dynamics and thus cannot perform work or useful functions. Designing such a system to choose a specific dynamical state is a formidable challenge. Motivated by recent advances enabling optogenetic control of experimental active materials, we describe an optimal control theory framework that identifies a spatiotemporal sequence of light-generated activity that drives an active nematic system toward a prescribed dynamical steady state. Active nematics are unstable to spontaneous defect proliferation and chaotic streaming dynamics in the absence of control. We demonstrate that optimal control theory can compute activity fields that redirect the dynamics into a variety of alternative dynamical programs and functions. This includes dynamically reconfiguring between states, selecting and stabilizing emergent behaviors that do not correspond to attractors, and are hence unstable in the uncontrolled system. Furthermore, our results provide a roadmap to leverage optical control methods to rationally design structure, dynamics, and function in a wide variety of active materials.

Complex systems theory↗
DOE OSTI2024

Impact of Inverter-Based Resources on Grid Protection: A Review of Negative-Sequence Current Generation

The increasing integration of inverter-based resources (IBRs) in power grids poses challenges to traditional protection systems, primarily due to their different fault current signatures compared to conventional synchronous generators. Unlike synchronous generators whose fault response is dictated by their physical design, IBRs exhibit a wide range of fault characteristics due to manufacturer-specific control algorithms and settings. This dependence on proprietary control schemes makes modeling IBR behavior during faults significantly more complex, especially considering the rapid evolution of inverter technology and the diverse control strategies employed. While much research has focused on the positive-sequence current injections of IBRs during symmetrical faults, the understanding of negative-sequence current generation during non-symmetrical faults remains limited. This report provides an overview of current research on IBRs' negative-sequence current generation during unbalanced faults and its impact on protection schemes based on negative-sequence components. It covers both type III wind turbines and full-size converter-based IBRs. Additionally, this report reviews strategies for grid-forming controlled inverters to generate negative-sequence current during unbalanced faults, in addition to grid-following controlled ones.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2026

Surface Vacancy Engineering Re-Routes First-Cycle Redox for Stabilized Li-Rich Layered Cathodes

We demonstrate that atomic-scale surface disorder can control the first-cycle redox sequence of Li-rich layered oxides, eliminating the detrimental process of oxygen release and lattice collapse that degrades performance. In Li1.14Ni0.32Mn0.54O2 (LNMO), a simple chemical treatment introduces oxygen and transition metal (TM) vacancies confined to the particle surface while preserving the bulk layered framework. Multi-modal synchrotron analyses reveal that these vacancies trigger an early oxygen oxidation below 4.4 V, delay nickel oxidation to higher potential, and suppress the formation of covalent Ni4+─O states. This modified pathway prevents irreversible oxygen release, suppresses manganese dissolution, and maintains metal-oxygen coordination at high voltages. Consequently, the treated cathode delivers higher first-cycle Coulombic efficiency (CE), mitigated voltage fade, and superior capacity retention. By directly linking engineered surface disorder to redox reactions and associated structural transformations, this work establishes a general design principle for durable, high-energy-density cathodes.

Kang, Seongkoo↗
DOE OSTI2022

Structural basis of template strand deoxyuridine promoter recognition by a viral RNA polymerase

Recognition of promoters in bacterial RNA polymerases (RNAPs) is controlled by sigma subunits. The key sequence motif recognized by the sigma, the -10 promoter element, is located in the non-template strand of the double-stranded DNA molecule ~10 nucleotides upstream of the transcription start site. Here, we explain the mechanism by which the phage AR9 non-virion RNAP (nvRNAP), a bacterial RNAP homolog, recognizes the -10 element of its deoxyuridine-containing promoter in the template strand. The AR9 sigma-like subunit, the nvRNAP enzyme core, and the template strand together form two nucleotide base-accepting pockets whose shapes dictate the requirement for the conserved deoxyuridines. A single amino acid substitution in the AR9 sigma-like subunit allows one of these pockets to accept a thymine thus expanding the promoter consensus. Our work demonstrates the extent to which viruses can evolve host-derived multisubunit enzymes to make transcription of their own genes independent of the host.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Liquid-induced topological transformations of cellular microstructures

The fundamental topology of cellular structures—the location, number and connectivity of nodes and compartments—can profoundly affect their acoustic, electrical5, chemical, mechanical and optical properties, as well as heat, fluid and particle transport. Approaches that harness swelling, electromagnetic actuation and mechanical instabilities in cellular materials have enabled a variety of interesting wall deformations and compartment shape alterations, but the resulting structures generally preserve the defining connectivity features of the initial topology. Achieving topological transformation presents a distinct challenge for existing strategies: it requires complex reorganization, repacking, and coordinated bending, stretching and folding, particularly around each node, where elastic resistance is highest owing to connectivity. Here we introduce a two-tiered dynamic strategy that achieves systematic reversible transformations of the fundamental topology of cellular microstructures, which can be applied to a wide range of materials and geometries. Our approach requires only exposing the structure to a selected liquid that is able to first infiltrate and plasticize the material at the molecular scale, and then, upon evaporation, form a network of localized capillary forces at the architectural scale that ‘zip’ the edges of the softened lattice into a new topological structure, which subsequently restiffens and remains kinetically trapped. Reversibility is induced by applying a mixture of liquids that act separately at the molecular and architectural scales (thus offering modular temporal control over the softening–evaporation–stiffening sequence) to restore the original topology or provide access to intermediate modes. Guided by a generalized theoretical model that connects cellular geometries, material stiffness and capillary forces, we demonstrate programmed reversible topological transformations of various lattice geometries and responsive materials that undergo fast global or localized deformations. In conclusion, we then harness dynamic topologies to develop active surfaces with information encryption, selective particle trapping and bubble release, as well as tunable mechanical, chemical and acoustic properties.

42 ENGINEERING↗
DOE OSTI2022

Carrier recombination dynamics and temperature dependent optical properties of InAs–GaSb heterostructures

Heterostructures with two dissimilar materials could offer unprecedented properties if one can carefully synthesize these heterostructures with atomically smooth interfaces and reduced number of recombination centers. InAs/GaSb-based heterostructures have technological importance for long wavelength infrared photodetectors if one can synthesize these materials with high-optical quality and high-carrier lifetime. In this work, the InAs/GaSb heterostructures with a different number of heterointerfaces and growth conditions were grown by solid source molecular beam epitaxy using valved cracker sources for both arsenic and antimony. Precise control of growth parameters and shutter sequences enabled abrupt InAs/GaSb heterointerfaces, as supported by a high-resolution transmission electron microscopic study. The temperature and power-dependent optical properties by photoluminescence (PL) spectroscopic analysis of InAs/GaSb heterostructures with 4 and 28 heterointerfaces displayed donor to the acceptor and the exciton bound to complex defects (V Ga Ga Sb ) 0 . Since the optical transition in PL measurements serves to determine the quality of the material, and the observed excitonic transitions from these InAs/GaSb heterostructures is an indication of high-quality materials. The high-carrier lifetimes of 139 ns to 185 ns from InAs/GaSb heterostructures were measured using microwave photoconductivity decay (μ-PCD) technique at room temperature. The observed increase in carrier lifetime is due to the decreasing number of Ga-related carrier recombination centers or defect complexes. This is further supported by the PL spectroscopic study. In addition, the carrier lifetime with different injection levels is supported by Shockley–Read–Hall recombination. We report these InAs/GaSb heterostructures with high-optical quality and high-carrier lifetimes would offer a path for the development of high-performance infrared photodetectors.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Chirality reversal of magnetic solitons in chiral Cr 1/3 TaS 2

Ferromagnetism in two-dimensional (2D) materials provides an ideal platform to study emergent electromagnetic phenomena in low dimensions for future spintronics. In magnetic-element intercalated transition metal dichalcogenides, topologically nontrivial spin textures, such as chiral helimagnetic spin states and chiral soliton lattices, are realized due to the chiral lattice distortions induced by intercalated magnetic ions. Consequently, the magnetic chirality is predictably determined by the sign of antisymmetric exchange interaction (or Dzyaloshinskii–Moriya interaction, DMI) vector that is coupled to the underlying crystal chirality. Here, using cryogenic Lorentz phase microscopy, we directly observed the chirality reversal behavior of the chiral soliton lattices in Cr 1/3 TaS 2 across the structural defects. We show that a partial 1 T stacking in 2H-TaS 2 locally reduces DMI, leading to magnetic chirality reversal with direct atomic resolution imaging. Furthermore, our experimental results show that manipulation of stacking sequence provides a viable way to control the chirality of topologically nontrivial soliton lattices in 2D magnets.

2D materials↗
DOE OSTI2022

Tracking and Rejection of Biased Sinusoidal Signals Using Generalized Predictive Controller

Some novel applications require the tracking/rejection of biased sinusoidal reference/distur-bances. According to the internal model principle (IMP), a controller must embed the model of a biased sinusoidal signal to track references and also reject perturbations modeled through the aforementioned signal. However, the design of that kind of controller is not straightforward, especially when they are implemented in digital processors. This paper presents a controller, based on generalized predictive control (GPC), designed for tracking/rejection of biased sinusoidal signals. In general, GPC is based on the prediction of the plant responses through an augmented prediction model. The proposed approach develops an augmented model that predicts the future errors. The prediction model and the control law used in the proposed approach embed the discrete-time model of a biased sinusoidal signal. Thus, the proposed controller can track/reject biased sinusoidal references/disturbances. The predicted errors and the future inputs of the proposed augmented model are used to define the cost function that measures the control performance. An optimization technique was applied to obtain the solution of the cost function, which is the optimal sequence of future model inputs that allows defining the control law. Experimental tests prove that the proposed controller can asymptotically track and reject biased sinusoidal signals.

42 ENGINEERING↗
DOE OSTI2023

On the Low Risk of SSR in Type III Wind Turbines Operating with Grid-Forming Control

We have shown in previous work that the risk of subsynchronous resonance between wind power plants with Type III wind turbines and series-compensated transmission lines is low when the wind turbines are operated in grid-forming (GFM) mode instead of the standard grid-following mode. This paper explains the fundamental mechanism behind the improved damping characteristics by modeling the positive- and negative-sequence impedances of Type III wind turbines in GFM control mode. Here it is discovered that the GFM control naturally acts against the negative resistance behavior of Type III wind turbines at subsynchronous frequencies that results from an interaction between the rotor-side converter current controller and negative slip. The developed impedance models in the sequence domain and the improved damping behavior are verified using PSCAD simulations of a 2.5-MW Type III GFM wind turbine. The modeling predictions are also supported by experimentally measuring the impedance response of a 2.5-MW Type III wind turbine in GFM mode.

17 WIND ENERGY↗
DOE OSTI2022

Validation and functional characterization of transcription factors in wheat using cell-free protein expression and high-throughput sequencing technologies

Transcription factors (TFs) are critical biomolecules that control and regulate gene expression in every organism. In wheat, there are 3,606 genes annotated as putative TFs which are primarily uncharacterized. In this work, using a DAP-seq approach, we have validated and characterized a select number of TFs (5bl and 5dl) belonging to GeBP family of proteins, responsible for plant cellular growth, development, and differentiation. We found that top DNA binding motifs for 5bl and 5dl are (G/T)N(T/G)GTGGT and (C/G)AA(C/G)AA respectively. These motifs/peaks are enriched in the promoter regions of the genes, which are associated with rRNA biogenesis and protein maturation pathways. This study is also a first demonstration that DAP-seq can be applied for such a complex and large genome such as wheat.

59 BASIC BIOLOGICAL SCIENCES↗